1. Field of the Invention
The present invention relates generally to material processing mills having a pair of rotating rolls between which material is processed. More particularly, the present invention concerns an improved drive arrangement that provides relatively high drive efficiency and unprecedented durability.
2. Discussion of Prior Art
A material processing mill (e.g., a flaker or roller mill) traditionally includes a pair of rolls defining a nip therebetween. One of the rolls is traditionally shiftable relative to the other so that the size of the nip can be varied. This not only permits adjustment of the nip size, but a spring relief may be provided so that the shiftable roll is yieldably maintained in the desired position and can shift relative to the other roll when a large object passes through the nip. Those ordinarily skilled in the art will also appreciate that the actual manner in which material passing through the nip is processed depends on, among other things, the size of the nip, the configuration of the roll, the speeds of the rolls, etc. For example, a roller mill typically includes a pair of corrugated rolls that rotate at different speeds to comminute the material. On the other hand, a flaker mill normally uses smooth rolls rotated at the same speed to press the material into flakes, although some flaker mills use corrugated rolls such as those used in the cattle feed industry.
In any case, conventional material processing mills have heretofore utilized a single belt drive to rotate both rolls. The standard mill drive includes a single stationary motor and, because the rolls desirably rotate in opposite directions, a xe2x80x9cback-wrappedxe2x80x9d V-belt. In other words, the belt is disposed along a serpentine path
It has been determined that this drive arrangement presents numerous problems. For example, drive components, such as bearing assemblies and shafts, have been known to fail prematurely. Furthermore, the standard mill drive is believed to be terribly inefficient.
Responsive to these and other problems, an important object of the present invention is to provide a drive for rotating the rolls of a material processing mill that is more efficient than standard mill drives. It is also an important object of the present invention to provide a mill drive that does not prematurely fail. Another important object of the present invention is to provide a material processing mill having these drive advantages. Yet another important object of the present invention is to provide a mill drive that is durable, simple in construction, and inexpensive.
In accordance with these and other objects, the present invention concerns a material processing mill that includes a separate drive for each of rolls. Each drive includes a motor, a rotatable drive member drivingly connected to the motor, a rotatable driven member fixed relative to the respective one of the rolls, and an endless positive drive element that drivingly connects the driven member to the drive member. Contrary to initial thoughts, this dual drive arrangement provides numerous unexpected advantages. For example, the elimination of the serpentine belt arrangement (required in a single drive mill to reverse the rotational direction of one of the rolls) surprisingly saves cost and simplifies the construction, even though two separate drives are provided. Moreover, the positive drive element used in each of the drives is believed to significantly improve the transfer of power from the motor to the respective roll. It is further believed that the individual drives will enjoy significantly longer maintenance free operation than conventional mill drives. This is apparently attributable to, among other things, the fact that the positive drive belt does not require the same degree of tensioning as the standard V-belt. Yet another advantage is the that the user is given greater flexibility on controlling the relative rotational speeds of the rolls.
The present invention also contemplates the use of a unique motor base that shiftably supports the motor associated with the shiftable roll. The motor includes a carrier to which the motor is fixed so that the motor is free to shift while rotating the shiftable roll. The motor and shiftable roll are preferably interconnected by an element tensioning device that is operable to adjust the tension of the element drivingly connecting the roll to the motor. The tensioning device adjustably fixes the motor relative to the shiftable roll so that the spacing between the motor and the shiftable roll is selectively variable. Thus, the motor and the shiftable roll shift together except when the tensioning device is adjusted to vary the tension of the belt. Because the motor normally shifts with the roll, the tension of the element remains constant as the roll shifts to its various positions. That is to say, if the motor did not shift with the roll, the tensioning device would need to be configured to xe2x80x9cover-tensionxe2x80x9d the element when the roll is closest to the motor. This would ensure that the element would be sufficiently tensioned when the roll is furthest from the motor.
Other aspects and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments and the accompanying drawing figures.